The invention relates to a method for reconditioning foundry sand.
The wet, mechanical, thermal or combined regeneration of foundry sand such as quartz sand, olivine, zircon, chromite sand and the like having organic or inorganic binders is known. The goal of such regeneration processes is to provide a reconditioned sand which can be re-used instead of or as new sand. At the same time, substances in the foundry sand hazardous to the environment are to be eliminated by regeneration. Sand bound organically usually only needs to be regenerated thermally, if it does not contain basic, acidic or other disturbing components, which do not combust or vaporize.
Mono-sand or mixed sand bound inorganically, in particular sand originally treated with bentonite must be thermally and mechanically regenerated to produce a sand which can be re-used.
A disadvantage of these known methods, for example for organic binder systems with basic or acidic components which are difficult or impossible to eliminate and in particular for mono-sand or mixed sand with inorganic binders, is that the regenerate sand has properties which deviate from new sand, for example the pH-value, the electrical conductivity, the degree of oolithization, the sludge content and the like. The properties of such regenerate sand are more or less disadvantageous especially for reuse in making cores. The poorer properties of such regenerate sand apply particularly in its use as core sand with a synthetic resin binder and cause reduced rigidity, reduced processing time of the sand mixtures, increased consumption of binder and the like.